The present invention relates to the type of system disclosed in my earlier U.S. Pat. No. 4,042,863. In that system, a positioning motor is connected in a negative-feedback control network and, in dependence upon a speed signal and in dependence upon a displacement signal furnished by a displacement transducer, can be caused to stop at predetermined angular positions in the manner of a stepper motor, irrespective of whether the positioning motor is per se constructed as a stepper motor. A synchronizing diaphragm is coupled to the motor and moves through the light paths of a plurality of light detectors. In so doing, the synchronizing diaphragm causes each light detector to generate a respective signal component, the signal components being phase-shifted relative to each other or one another, and being combined to form the actual output signal of the displacement transducer system. In particular, the individual light detectors are individually activatable and are activated in sequences such that the individual signal components are combined to form the actual transducer-system output signal. The actuating signal applied to the positioning motor is derived from the transducer-system output signal, and includes a component proportional thereto and a component proportional to the time-derivative of the transducer-system output signal.
In this type of system, each of the signal components of the displacement transducer output signal corresponds to a different angular position to which the rotor of the positioning motor can be moved. The synchronizing diaphragm is provided with cyclically repeated circumferentially extending markings, and the density of angular spacing of the cyclically repeated markings determines the number of angular positions at which the rotor of the positioning motor can be stopped. In terms of production, limitations upon the density of such angular spacing place limits upon the number of selectable angular positions at which the positioning motor of the system can be stopped.